I'm having a problem with my 748 at the moment, it starts and ticks over fine but when you rev it, it feels like it is only running on 1 cylinder. I have hooked it up to a ducati diagnostic tester and it shows a air pressure sensor fault. I'm going to strip it down tomorrow and test the sensor and replace if needed. I'm just wondering if anyone else has ever had this sensor fail and if so what symptoms did you experience?
Marc, mine went down but it only did it on very hot days when the engine was hot and the rad fan was about to kick in. It would start to lose one cylinder and then the other over about a mile and broke down three days on the trot, two at exactly the same point on my way home from work. The break down started with one cylinder stopping firing followed after a short distance with the other missing and the engine not responding to the throttle, barely running at all on tick over and missing under load whilst trying to pull away. It took a while to diagnose. I noticed the boot over the connector plug had perished and it was obvious with the plug out that water had been sitting in the plug socket and had caused white oxide corrosion on the two left hand connector pins (when sat on the bike). Water had got in and when the bike was on its side stand being washed probably, the water sat in the lowest corner of the socket. It was later confirmed by Rich Llewellyn on his diagnostic tester. Since a new one was fitted the bike has gone better than ever.
Mine used to play up exactly the same as you describe, I used to be able to turn it off and on a few times and then it would be ok. I never did get to the bottom of the problem and no errors were ever stored in the ECU. It's only now that the problem is constant that the air pressure sensor error is showing up on the ECU. Hopefully that's all it is My rubber boot around the connector is perished too, I guess that's what has caused the damage.
Well, I replaced the air pressure sensor with a spare one I had and that has eliminated error that the ECU kept reporting. Unfortunately I still have a lack of power, so I guess that wasn't the full problem. Although it does seem to be running slightly better with the new(different) sensor it still feels like it is running on one to one and a half cylinders. I'm now trying to find which cylinder has the problem, I disconnected the horizontal cylinder's spark plug lead and tried to start her but she would not have it, it didn't even sound like the other cylinder was trying to fire, so hopefully I have determined that the problem is with the vertical cylinder. So it's off with the tank again! today and repeat the test. I'm assuming the engine would start on one cylinder yeah? Could anyone confirm this? The mathesis tester is not showing any errors when I run a diagnostic test on the coils or injectors, but I'm not sure if the test would pick up a "down on power" coil or injector or is it a case of, yes it works or no it doesn't test?, does anyone know the answer to this?
I had a similar issue on my old 848. Bike should start on one cylinder... Unless it's the faulty one I did the same swapy roundy test to isolate the problem. Have you tried resting the plug on the head and hitting the start button to check for a spark? Not always a 100% reliable test of a "good" plug, but it's a good start...:smile:
That's the plan for today Nelson, It's such a pain in the a*se doing anything like this, what with having to keep taking the fuel tank and airbox off, then changing something, then putting the tank/airbox back on and testing it. I definitely need to make some extension fuel pipes up so I can run the bike with the tank off
Air box off? With mine you can carefully either prop the tank up at the rear, or turn at a slight angle to get at the vertical plug/run the bike.
Yeah you're right, I will be able to do what you say in order to test the vertical plug, I was thinking beyond that when it comes to checking/changing coils, leads and injectors etc :-(
Ah -gotcha. I'm sure I saw an old post/pic somewhere, where the seat unit had been removed and the tank turned around then strapped to the rear sub-frame. Might be worth a fiddle? Will it run with no tank? (748/916/996/998) - Ducati.ms - The Ultimate Ducati Forum
can definitely be run if fuel hoses standard/unsnagged but easiest with two people. Would be good to do a compression test while you are there (and for peace of mind just swap the plug for a new one anyway after tests performed)
I would love to do a compression test, unfortunately someone borrowed my compression tester a year or two ago and I haven't seen it since...grrrrrrrrrr!
UPDATE Right, I removed the HT lead from the vertical cylinder and no change, the bike started and ticked over exactly the same as when it was connected. Great! The problem is with the vertical cylinder. Attached a spare spark plug and it gave a good normal spark, So I removed the existing spark plug and tried that one, not very good at all, it sparked but only between the threaded part and the engine it was laying on, no spark at the electrode at all. So it seems(hopefully) the plug was duff. Just waiting for the battery to charge up now so I thought it was tea break time
Well that didn't last very long :-( I've done about 10 miles since replacing the spark plug and it has been running perfect. Started her up this morning and she is running on one cylinder again. So, tank off yet again, checked the spark plug and once again only sparking between plug body and engine casing(not electrode) so I checked with a different spark plug and yes it's sparking properly. Granted I am using some old spark plugs that were changed a while ago(even though they were ok) but surely they should last longer than 10 miles, there is obviously a problem elsewhere that's killing these plugs. My first thoughts are the coil, I have tested the coil using the mathesis tester but it is not showing any error. Is there any other way of testing the coil? Could the HT lead be causing this problem? Any thoughts anyone?
definitely change the Ht lead now Marc - the front cylinder is usually the first to give lead problems but you can never rule out the same for the rear. A lead can decide to short to earth occasionally usually when constantly damp in one place from condensation etc. A weakness develops and a spark will then begin to jump at the slightest excuse particularly with the type of resistor plugs that are the norm of today. Often the only cure is to replace the lead as it eventually becomes permanently damaged - an isolated black residue being one of the clues. To be thorough here, I would still check and clean all the ignition related connectors leading to that cylinder and (despite your OK test result) even swap coils to at least cross this off the list incase it is breaking down intermittently.
Thanks Chris. I will swap the coils around now and see if the problem moves to the front cylinder. I'll also swap the rear HT lead, I have a spare one(not new tho) here. It's probably time I bought some new HT leads, would you recommend I get OEM ones or is there a good/cheaper alternative?
nothing wrong with just replacing with original - they were parts bin Lancia Integrale at one point but these may be dubbed 'obsolete' via Fiat dealers now. I have used Magnecor before but for me, the quality of the lead (and there are many - NGK is another) is overtaken by the need to seal the 'spark plug tube' efficiently* - particularly with the front cylinder, and a lot of the non - O.E.M. are poor in this area. *if you ride in the dry 99% of the time then you could ignore this
